Electric resistance heating element and method of making the same



Oct. 29., 1940. J. G LAMPE ET AL 2,219,523

ELECTRIC RESISTANCE HEATING ELEMENT AND METHOD OF MAKING THE SAME Filed July 17, 1957 2 Shets-Sheet 1 FIG 2.

JAMES (3.. LAMPE RQBEQTJ. Kama ZNVENTORS MM M 0W0 ATTORN EY$ Oct. 29. 1940. J. G LAMPE ET AL ELECTRIC RESISTANCE HEATING ELEMENT AND METHOD OF MAKING THE SAME Filed July 17, 1937 2 Sheets-Sheet 2 FIG 10 FIG 11 4 JAMES G. LAMPE PosERTlKma INVENTORS ATTORNEYS Patented Oct. 29, 1940 UNITED STATES PATENT OFFICE ELECTRIC RESISTANCE HEATING ELEMENT AND METHOD OF MAKING THE SAME Application July 17, 1937, Serial No. 154,268

13 Claims.

This invention relates to electric resistance heating, and the principal object of the invention is to provide a new and improved heating element and a new and improved method of making thesame.

In the drawings accompanying this specification and forming a part of this application, we have shown, for purposes of illustration, several forms which our invention may assume, and in these drawings:

Figures 1, 3, 5, and 7 are longitudinal sectional fragmentary views illustrating steps in the method of producing an electrical resistance heating element in accordance with our invention, Figures 2, 4, 6, and 8 being sections taken on correspondingly numbered lines of Figures 1, 3, 5, and 7 respectively,

Figures 9 and 10 are sectional views illustrating another embodiment of a heating element that may result from our method, Figure 9 being a section taken on the line 99 of Figure 10, and Figure 10 being a section taken on the line |0|0 of Figure 9,

Figures 11 and 12 show diiferent forms of resistors, which may be used in the embodiment of Figures 9 and 10,

Figures 13 and 14 are cross sections of still other forms of resistance heating elements produced in accordance with our invention,

Figures 15 and 16 illustrate still another form of heating element produced in accordance with our invention, Figure 15 being a transverse section and Figure 16 being a section taken along the line |6|6 of Figure 15 looking in the direction of the arrows.

Referring first to Figures 1 through 8, the method of producing the electrical resistance heating element here illustrated includes first forming an insulating chamber within a metal sheath, desirably seamless, and one way in which this may be accomplished as illustrated in Figures 1 through 4 is by introducing a mandrel 20 of desired form into a metal sheath 2|. The mandrel 20 is here shown as having a portion 22 of square cross sectional outline which fits within the inside wall of the sheath 2|, the sheath 2| being here shown as of circular cross section. In the particular instance illustrated the mandrel has an end portion 23 which is cylindrical and fits the inside wall of the sheath 2|.

After the mandrel 20 has been introduced into the sheath electrical insulating material 24 (see Figures 3 and 4) of suitable form is introduced, in any suitable way, desirably by extrusion, into the spaces 25 (see Figure 2) left between the the insulating chamber 26, a further quantity mandrel and the inside wall of the sheath. The material 24 may comprise silica, silicates, aluminum oxides, or any refractory oxide or combination of refractory oxides, or any other suitable refractory material, and the material may 5 be mixed with a chemically unstable refractory oxide to act as a bond on hydration, or mixed with a clay, or with any other suitable binder. For the sake of brevity refractory insulating materials suitable for use in our method may be termed plastoid.

After the plastoid insulating material 24 has been introduced in the spaces 25 between tre mandrel 22 and the sheath 2|, the mandrel removed leaving the plastoid insulating material 15 24 to form an insulating chamber 26, in this instance of square cross sectional outline, as shown in Figure 4, within the sheath. The plastoid insulating material is of course of such character that it is to a desired degree self sustaining as to form, so that the mandrel may be withdrawn. leaving the material to form the chamber 26. The cylindrical portion 23 of the mandrel leaves a short end portion of the sheath empty in the illustrated instance, but that is not essential.

In the instance illustrated, there is now introduced within the insulating chamber 26, a resistor 21 which is here shown as a helix formed of resistance wire, and the wire desirably has suitably welded thereto at both of its ends lead-in terminals, one of which, 28, may be seen in Figure 5. The resistor is desirably of such size that it fits slidably into the chamber 26.

After the resistor 21 has been introduced into of plastoid insulating material 29 may be extruded into the insulating chamber 26 and about the resistor 21, so as to fill the chamber and embed the resistor as shown in Figures 7 and 8. However, preferably, the refractory insulating 40 material, 29, which is introduced into the chamber 26 after the resistor 21 has been introduced therein, is of granular, pulverulent, or comminuted form, and of such character that it may be compacted by vibration or in any other suit- 45 able way. It will be understood that the material in such form may also be mixed with a suitable binding material. In either case the insulating material 29 may also be termed plastoid, since it has the mechanical characteristics of impressionability and fluency, as of a plastic, when it is introduced into the chamber 26, though it may be compacted to a hard mass.

In case that a space 30 is left at the ends of the sheath 2|, this space may serve to receive 5 any suitable form of insulation (not shown) for supporting the conductor 28 or any suitable form of terminal (not shown) to which the conductor 23 may be connected. as shown, for example, in the patent to Wiegand 1,997,844, April 16, 1935. However, those skilled in the art will understand that the details of the terminal construction in any embodiment of our invention will depend upon the shape and form of the heater, and the particular terminal design will depend upon considerations for use or production, and that the terminals may Project axially through the end openings of the sheath or through any other suitable opening provided therein. These details, per se, form no part of our invention.

Heating elements of the type herein disclosed are adapted to be pressed externally, or they may be compacted interiorly .and exteriorly, and if desired they may be formed in the act of pressing into any suitable desired cross-sectional shape, both for the purpose of increasing the compaction of the insulating material within. the sheath and for the purpose of specially forming or shaping the sectional shape of the element,

and they may be bent across their longitudinal axes to desired configurations.

It will accordingly be understood that while a heating element such as illustrated in Figures 7 and 8 is utilizable in the form there illustrated, it may be'worked into other forms to bring the sheath to a cross sectional outline diflerent from the initial cross sectional outline, and the element bent with respect to the initial longitudinal axis to any suitable and desired shape.

It will be evident that the hereinbefore described method permits the positive location of the resistor within the sheath by means of the preformed insulating chamber.

Another embodiment of a resistance heating element produced in accordance with our invention is illustrated in Figures 9 and 10. The element has a metallic sheath 3| the initial cross sectional outline of which, in this instance, is of oblong rectangular form, and the final form may be the same or different. It will be evident that in this instance two mandrels or a mandrel having two spaced parallel portions (not shown) each corresponding to the portion 22 of the mandrel 20 illustrated in Figures 1 and 2, may be utilized to form two axially extending insulating chambers 34, 35 within the sheath 3|, by the introduction of plastoid insulating material 36 in the spaces between the mandrel and the inner wall of the sheath 3|, and also between the juxtaposed faces of the mandrel portions to form a dividing wall 31. If desired, this divi g wall 31 may have an end 38 terminating a edetermined distance short of one end of the insulating chambers 34, 35, so that a bent part 39-01 a helicalresistor 40 may be disposed to cross over from one of the chambers 34, 35, to the other. The resistor 40 may be of the form shown in Figure 11, one of the parts, 4|, of the resistor.

being in the chamber 34 and the other part, 42, of the resistor being in the other chamber, 35. The ends of the helical resistor 40 are thus brought to the same end of the sheath 3|, and

any suitable terminal means may be provided if the two parts of the resistor 43 being in this instance straightened out, and this resistor being particularly adapted for use where the division wall 3! is not countersunk.

It will be understood that after the resistor 40 (or 43) is inserted in the two chambers, 34, 35, a further quantity of suitable insulating material 32 is desirably introduced in each chamber, as hereinbefore described in cdnnection with the insulating material 29 introduced in the chamber 26 of Figure 4.

In Figure 13 is shown a cross section of another embodiment of a resistance heating element in which n insulating chamber 45 is formed within a meta lic sheath 48, the cross sectional outline of the inside wall of the chamber 45, as well as of the sheath 45, being in this instance circular. This insulating chamber 45, is formed in the same way as described in connection with Figures 1 through 4, a mandrel (not shown) of circular cross section being however used. After the insulating chamber 45 has been formed a resistor 41 is introduced into the chamber 45, the resistor 41 being in this instance of helical form fitting in the chamber 45. The resistor 47 may be disposed, before introduction into the chamber 48, on a self-sustaining body of friable refractory insulating material 48, which in this instance may be in the form of a rod or stick of cylindrical form. On the other hand, the rod or stick 48 may be introduced within the resistor 41 after the resistor has been introduced into the chamber 45, the size and configuration of the stick being of course made suitable to that end. The resistor 47 may have its ends connected to leadin conductors disposed at opposite ends of the sheath, such as the lead-in conductors 28 of Figures 5 and 7, or the rod of friable insulating material 48 may be provided with a longitudinally extending hole 49 through which a straightened out end portion 50 of the helical resistor 41 may be inserted, so as to bring the ends of the resistor to the same end of the sheath 43. The stick or rod 43 may be composed of refractory insulating material of the same characters as the material 29 but brought to a self-sustaining form as by compaction, or it may be of any other suitable refractory material which is friable.

Desirably a heating element such as described in connection with Figure 13 will be pressed in any suitable way, to any suitable form, so that the friable insulating material 48, and also the insulation formingthe insulating chamber 45 will be thoroughly compacted about the resistor 41 to take up any voids.

In Figure 14 is shown another embodiment of a resistance heating element, an insulating chamber 5| having an inner wall of square cross sectional outline being first formed in a metallic sheath 52, as described in connection with Figures 1 through 4. Within the insulating chamber 5| is disposed a resistor 53 which may be helical, and within the resistor 53 is a rod or stick of friable insulating material 54, here shown as of generally square cross sectional outline fitting within the resistor 53. The resistor 53 and the stick of friable insulating material 54 may be introduced into the chamber 5| in any of the ways already described in connection with Figure l3, and thereafter insulating material 55, of any of the forms described in connection with the insulating material 23 of Figures 7 and 8 is introduced in the spaces between the stick 54 and the inside wall of the insulating chamber 5|, so as to embed the resistor. If desired, the stick of friable insulating material 54 may be provided with a longitudinally extending hole 58, here shown as of square cross sectional outline, and a straightened portion 51 of one end of the resistor helix may be disposed through this hole, as described in connection with the resistor portion 50 shown in Figure 13. At the time that the insulating material 55 is introduced, some of the same insulating material may be simultaneously introduced in the space between the resistor portion 51 and the inside walls of the hole 58.

The heating element shown in Figure 14 also may be compactedand worked to any desired form in the manners hereinbefore described.

In Figures 15 and 16 is shown a resistance heating element in which is utilized a resistor 58, comprising a zig-zag ribbon of resistance material. The heating element is here shown as comprising a metallic sheath 59 of generally oblong rectangular cross sectional outline in which is formed an insulating chamber 50 here shown as of elongated cross sectional outline. The length of the cross section of the chamber 50 is long enough to receive the zig-zag resistor 58, and the cross section of the chamber is wider at its central portion than the width of the ribbon constituting the resistor 58. It will be evident that the chamber 60 is so formed that the resistor 58 may be readily introduced therein, and the resistor is positively positioned by the narrow ends of the chamber while spaces are left between the wide side walls of the chamber and the resistor. After the insulating chamber 50 is formed within the sheath 59, in the manner described in connection with Figures 1 to 4, the resistor 58 may be introduced into the chamber, and then refractory insulating material 6| may be introduced in the spaces between the inside wall of the chamber 60 and the resistor 58 in the same way that the insulating material 29 is introduced in the case of the embodiment of Figures 7 and 8. As in the previously described embodiments, a heating element, such as shown in Figures 15 and 16, may be suitably worked to compact the insulating material within the sheath about the resistor.

It will be apparent that our method is adapted for the production of resistance heating elements in which the sheath may be any desired initial cross sectional outline, and that if desired the elements may be pressed or otherwise worked so that the final cross sectional outline of the sheath may be substantially different in form from the initial outline or it may be of the same or similar form. And, further, that the resistor may be of any desired or suitable form. Also, the elements may have rectilinear longitudinal axes in their final form, or the elements may be bent or otherwise worked so that in the final form the longitudinal axes are non-rectilinear.

From the foregoing it will be apparent to those skilled in the art that each of the illustrated embodiments of our invention provides a new and improved electrical heating element produced in a new and improved manner, and accordingly, the principal object of our invention is accomplished. On the other hand, it also will be obvious to those skilled in the art that the described and illustrated methods and heating elements may be variously changed and modified, or features thereof, singly or collectively, embodied in other steps or embodiments than those described and illustrated, without departing from the spirit of our invention, or sacrificing all of the advantages thereof, and that accordingly, the disclosure herein is illustrative only, and our invention is not limited thereto.

We claim:

1. The method of producing a tubular electric heating element, which comprises: introducing plastoid heat-conducting electrical-insulating material into a tubular metallic sheath, into space between mandrel means and said sheath, and forming, on at least part of the inner surface of said sheath, lining comprising said material in self-sustaining condition and conforming to and in heat-transfer contact with the apposite inner surface of said sheath; and introducing a resistor section in spaced relation to said sheath, spaced from said sheath at least in part by said lining.

2. The method of producing a tubular electric heating element, which comprises: introducing plastoid heat-conducting electrical-insulating material into a tubular metallic sheath, into space between mandrel means and said sheath, and forming, on at least part of the inner surface of said sheath, lining comprising said material'in self-sustaining condition and conforming to and in heat-transfer contact with the apposite inner surface of said sheath; and introducing a 'resistor section in spaced relation to said sheath, spaced from said sheath at least in part by said lining, and at least partially embedding said section.

3. The method of producing a tubular electric heating element, which comprises: introducing plastoid heat-conducting electrical-insulating material into a tubular metallic sheath, into space between mandrel means and said sheath, and forming, on at least part of the inner surface of said sheath, lining comprising said material in self-sustaining condition and conforming to and in heat-transfer contact with the apposite inner surface of said sheath; and introducing additional heat-conducting electrical-insulating material, and a resistor section in spaced relation to said sheath, spaced from said sheath at least in part by said lining.

4. The method of producing a tubular electric heating element, which comprises: introducing plastoid heat-conducting electrical-insulating material into a tubular metallic sheath, into space between mandrel means and said sheath, and forming, on at least part of the inner surface of said sheath, lining comprising said material in self-sustaining condition and conforming to and in heat-transfer contact with the apposite inner surface of said sheath; and introducing non-plastoid heat-conducting electrical-insulating material, and a resistor section in spaced relation to said sheath, spaced from said sheath at least in part by said lining.

5. The method of producing a tubular electric heating element, which comprises: introducing plastoid heat-conducting electrical-insulating material into a tubular metallic sheath, into space between mandrel means and said sheath, and forming, on at least part of the inner surface of said sheath, lining comprising said material in self-sustaining condition and conforming to and in heat-transfer contact with the apposite inner surface of said sheath; introducing a resistor section in spaced relation to said sheath, spaced from said sheath at least in part by said lining; and thereafter introducing additional heat-conducting electrical-insulating material.

6. The method of producing a tubular electric heating element, which comprises: introducing plastoid heat-conducting electrical-insulating material into a tubular metallic sheath, into space between mandrel means and said sheath,

and forming, on at least part of the inner surface of said sheath, lining comprising said material in self-sustaining condition and conforming to and in heat-transfer contact with the apposite inner surface of said sheath; and introducing additional heat-conducting electrical-insulating material while said lining is in plastoid condition, and a resistor section in spaced relation to said sheath, spaced from said sheath at least in part by said lining.

'7. The method of producing a tubular electric heating element, which comprises: introducing plastoid heat-conducting Y electrical-insulating material into a tubular metallic sheath, into space between mandrel means and said sheath, and forming, on at least part of the inner surface of said sheath, lining comprising said material in self-sustaining condition and conforming to and in heat-transfer contact with the apposite inner surface of said sheath; and introducing a resistor section in spaced relation to said sheath, spaced from said sheath at least in part by said lining, and reducing the element in cross-section over at least part of the longitudinal extent of said resistor section.

8. The method of producing a tubular electric heating element, which comprises: introducing plastoid heat-conducting electrical-insulating material into a tubular metallic sheath, into space between mandrel means and said sheath, and forming, on at least part of the inner surface of said sheath, lining comprising said material in self-sustaining condition and conforming to and in heat-transfer contact with the apposite inner surface of said sheath: and introducing a resistor section in spaced relation to said sheath, spaced from said sheath at least in part by said lining, and reducing the element in cross-section over at least part of the longitudinal extent of said section, and at least partially embedding said resistor section.

9. The method of producing a tubular electric heating element, which comprises: introducing plastoid heat-conducting electrical-insulating material. into a tubular metallic sheath, into space between mandrel means and said sheath, and forming, on at'least part of the inner-surface of said sheath, lining comprising said material in self-sustaining condition and conforming to and in heat-transfer contact with the apposite inner surface of said sheath; and introducing additional heat-conductingelectrical-insulating material, and a resistor section in spaced relation to said sheath, spaced from said sheath at least in part by said lining,'and reducing the element in cross-section over at least part of the longitudinal extent of said resistor section.

10. The method of producing a tubular electric heating element, which comprises: introducing plastoid heat-conducting electrical-insulating material into a tubular metallic sheath, into space between mandrel means and said sheath, and forming. on at least part of the inner surface of said sheath, lining comprising said material in self-sustaining condition and conforming to and in heat-transfer contact with the apposite inner surface of said sheath; and introducing additional heat-conducting electrical-insulating material while said lining is in plastoid condition, and a resistor section in spaced relation to said sheath,

spaced from said sheath at least in part by said lining, and reducing the element in cross-section over at least part of the longitudinal extent of said resistor section.

11. The method of producing a tubular electric heating element, which comprises: introducing plastoid heat-conducting electrical-insulating material into a tubular metallic sheath, into space between said sheath and mandrel means transversely positioned with respect to said sheath at at least one placeintermediate the end portion of said sheath, and forming lining comprising said material, apposite at least part of the inner surface of said sheath; and introducing a resistor section in spaced relation to said sheath. spaced from said sheath at least in part by said lining.

12. The method of producing a tubular electric heating element, which comprises: introducing plastoid heat-conducting electrical-insulating material into a tubular metallic sheath, into space between said sheath and mandrel means transver'sely positioned with respect to said sheath at least at a plurality of spaced places intermediate the end portions of said sheath, and forminglining comprising said material, apposite at least part of the inner surface of said sheath; and introducing a resistor section in spaced relation to said sheath, spaced from said sheath at least in part by said lining.

13. The method of producing a tubular electric heating element, which comprises: introducing plastoid heat-conducting electrical-insulating material into a tubular metallic sheath. into space between said sheath and mandrel means in effect polygonal in cross-section and transversely positioned with respect to said sheath by abutment of the corners against the inner surface of said sheath, and forminglining comprising said material, apposite at least part of the inner surface of said sheath; and introducing a resistor section in spaced relation to said sheath, spaced from said sheath atleast inpart by said lining.

JANIES G. LAMPE. ROBERT J. KING. 

